CLARK : DISTRIBUTION OF CRINOIDS 



81 



one species {Psathyromeira erythrizon) derived from the Pacific 

 to the northeastward. 



The oceanographic conditions in both of these divisions of the 

 Arctic province are practically identical ; but the f aunal differences 

 are such as to suggest that they never have been parts of the 

 same fauna since the present distribution of land and sea became 

 established. 



Hathrometra prolixa is probably an intruder into the Arctic 

 Ocean from the Atlantic under the present conditions, and the 

 same is undoubtedly true of Thaumatometra tenuis and Psathyro- 

 meira erythrizon in the Okhotsk and Japanese Seas. 



Judging from what we know of the fauna of the great Russian 

 lakes, Aral, Balkash and Baikal, as well as of the lesser lakes be- 

 tween them, it appears not improbable that this region was the 

 original home of Heliomeira, which it reached from the southward, 

 and from which, long ago, it spread both northward and east- 

 ward to the Arctic Ocean and to the Seas of Okhotsk and Japan; 

 but there must always be kept in mind the very remote possi- 

 bility that Heliomeira reached the Okhotsk and Japanese Seas 

 from the Ai*ctic Ocean by way of the Bering Strait and the coast 

 of Kamchatka, by some means divesting itself on the way of its 

 inseparable Arctic companion, Haihrometra prolixa. 



The bathymetric range of the three Arctic crinoids : 



Heliomeira glacialis. . 

 Hathrometra prolixa. 



fathoms 

 2-755 

 10-1088 



I Iyer inns carpenterii. 



fathoms 



755-1563 



The bathymetric range of the eighteen Antarctic crinoids: 



fathoms 



Thalassometra hispinosa 1600 



Psathyromeira aniarctica 1430 



Eumorphomeira hirsuia. 140 

 Eumorphomeira concin- 



na 211-222 



Promachocrinus kerguel- 



ensis 10-222 



Solanomeira aniarctica . 75-150 



Anihometra adriani. . . . 124-500 



Floromeira magellanica 17-782 



Hathrometra exigua. . . . 50-140 



fathoms 

 Trichometra remoia. . . . 1600 



Isometra angusiipinna . 56-600 

 Thaumatometra ahyssor- 



um 1600 



Bathymetra carpenteri . . 2600 



Thaumatocrinus renova- 



tus 1347-1800 



Ilycrinus australis 1375-2575 



Ptilocrinus brucei 2485 



Ptilocrinus antarciiciis . 266 



Hyocrinus hethellianus . 1600-2575 



